Axially adjustable thrust bearing for jet propulsion units

ABSTRACT

The present invention relates to a jet propulsion unit ( 1 ) for propulsion of a waterborne craft comprising at least one impeller pump ( 3 ) with a pump housing ( 4 ) in which an impeller shaft ( 22 ) or ajournal ( 21 ) connected to said impeller shaft ( 22 ) is rotatably journalled in bearings, and an impeller ( 7 ) blades ( 24 ), the impeller ( 7 ) being fixed to said impeller shaft ( 22 ) or journal ( 21 ) so as to follow the rotation of the impeller shaft ( 22 ), the impeller blades ( 24 ) being arranged at the impeller ( ) with a play of the blades ( 25 ) between each impeller blade ( 24 ) and the inside ( 15 ) of the pump housing ( 4 ). According to the invention the jet propulsion unit ( 1 ) also comprises an axially adjustable thrust bearing ( 27 ) arranged to cooperate with the impeller shaft ( 22 ) for adjusting said play ( 25 ).

TECHNICAL FIELD

[0001] The present invention relates to a jet propulsion unit forpropulsion of a waterborne craft comprising at least one impeller pumpwith a pump housing in which an impeller shaft or a journal connected tosaid impeller shaft is rotatably journalled in bearings, and animpeller, having impeller blades, the impeller being fixed to saidimpeller shaft or journal so as to follow the rotation of the impellershaft, the impeller blades being arranged at the impeller with a playbetween each impeller blade and the inside of the pump housing.

[0002] STATE OF THE ART AND PROBLEM

[0003] Jet propulsion units, also named water jet- or impeller units, ofthe aforedescribed kind are known in many different designs anddimensions, from smaller units of about 500 kW up to large units ofabout 30 000 kW and more. Compared to a conventional propeller, a waterjet unit has a method of propulsion that is to a great extent different.Instead of the conventional propeller it has a water pump or impellerpump, as it is called, mounted at the hull of the craft. The impellerpump comprises an impeller mounted within an enclosing, an impellerchamber, that is a part of a seawater flow tube at the same time. Theimpeller is attached to the end of a drive shaft, the impeller shaft,which is either the engine shaft of the craft or indirectly connected tosaid shaft. The purpose of the impeller is to pressure the seawatercreating a very forceful water jet, from that the name jet propulsionunit.

[0004] The force of reaction that results from the water leaving thepump is used to propel the craft. The direction of rotation of theimpeller is never changed but instead a separate “reversing device” isused for deflecting the direction of the water jet and thereby also thedirection of the force of reaction, which then also changes thedirection of the propulsion of the ship. A water jet unit has manyadvantages compared to a conventional propeller since an impeller pumphas an efficiency of up to 90% and more at speeds over 25 knots. Thisresults in higher speed of the craft at the same propulsion force ormarkedly lower fuel consumption at constant speed and lower propulsionforce.

[0005] However, today there is still a big gap between on one hand fastbut expensive airfreight and on the other hand cheaper but slowercontainer freight by ship. Therefore, there is a desire to be able tobuild very large and very fast ocean-going ships for high-speedtransports between for example USA and Europe and such ships would beequipped with very large water jet units. Such ships are estimated toreach average speed of 35 knots even at waves at the height of 7.5 meterand the present time of transport is estimated to be shortened by athird. To be able to bring about above mentioned ships, water jet unitsare needed that can reach at least 50 000 kW and that will have adiameter of intake of about 3.25 meter compared to the presently knownlargest diameter of 2.0 meter. The planned ships have units with a flowequivalent to about 500 m³ per second. It will be understood thatenormous units are required to manage this capacity.

[0006] However, larger installations need a higher accuracy at thechoice of the correct dimension of the water jet, both for achieving anoptimised efficiency and for improvement of the fuel economy. Othercommon demands on the propulsion unit may be for example goodmanoeuvrability and also the ability to handle tough operationsituations such as high sea. Several cooperating factors will decide howwell the ship will adapt to the demands made on it.

[0007] By controlling the play between the impeller blades and theimpeller chamber the risk that one runs of them contacting each otherwill be substantially reduced during normal operation, thus resulting inthat a higher efficiency of the impeller may be obtained. Thus, the playbetween the impeller and the impeller chamber is of great importance tothe propulsion output and since a bigger play reduces the efficiency ofthe impeller pump it is essential that the play is as small as possible.At a planned impeller pump the impeller blades will have a diameter ofabout 4.5 meters and the planned play between the impeller blades andthe impeller chamber will amount to only about 4 millimetres. It isunderstood that e.g. temperature variations, entails problems that makeit difficult to further reduce the play without the hazard ofbreakdowns. The damages that might be the result of the impellercontacting the enclosing are a serious problem. Such contact may be dueto e.g. the vibrations or oscillations caused by cavitation. If, forthis reason, the play instead is doubled, that is from about 0.1% of thediameter to 0.2%, the propulsion output will be reduced by about 1%which involves a not negligible increase in costs.

[0008] Because of the gains, calculated as a percentage, that can beobtained for each millimetre closer play that can be achieved, it isthus of utmost importance that the play normally can be kept with asnarrow margins as possible. Of course, at the same time, the demand onthe maximally admissible tolerance between the impeller and theenclosing will be very highly put forward. Furthermore, it is also truethat the larger jet propulsion unit, the larger the demands on thetolerance between different parts will be made. If calculated as apercentage, the machine tolerances of an impeller are higher than thoseof a clockwork. For example, impeller blades with a diameter of up to4500 millimetres are being turned and grinded with a precision of a fewtenths of a millimetre. At speed of for example 40 knots, these smalltolerances optimise the transformation of shaft-force intodriving-force, prolonging the endurance and giving minimal vibrationsand sound-levels.

[0009] However, one runs the risk that the oscillations and vibrationsat some occasions, for example, when strange objects pass through thepump, will cause such a radial movement of the blades of the impellerthat they will come in contact with the impeller chamber. The risk ofdamages that one runs will increase strongly at tough weatherconditions, for example, at high sea one runs the risk of largeacceleration or air suction through the pump. Also, the position of theimpeller can be altered because of movements in the hull of the shipitself. The consequences of a breakdown of the jet propulsion unitduring whole gale, in the middle of the Atlantic Ocean, could beserious.

[0010] Thus, it might be necessary to accept a somewhat reducedefficiency by increasing the play a little, at certain specialsituations. Since the impeller chamber and the impeller blades have aconical interface the play can be altered if the impeller is movedaxially. Thus, it is an essential demand that, when necessary, the playbetween the impeller and the enclosing can be adjusted by axial movementof the impeller.

THE OBJECT AND CHARACTERISTICS OF THE INVENTION

[0011] It is an object of the present invention to accomplish such a jetpropulsion unit for propulsion of ships, that makes it possible tosubstantially reduce or fully eliminate the risk of the blades of theimpeller contacting the inner wall of the impeller chamber and to beable to make use of the favourable qualities of the jet propulsion unitin a better way than before and also at considerable larger shipdimensions than at the present conventional dimensions of ships. It issuggested, as a solution of the complex of problems, that the thrustbearings included are movably arranged. The movement is suitably done byusing some sort of hydraulic piston arrangement, which also wouldcontribute with a certain dampening function.

[0012] The jet propulsion unit according to the invention ischaracterized in that the jet propulsion unit also comprises an axiallyadjustable thrust bearing arranged to cooperate with the impeller shaftfor adjusting said play.

[0013] According to further aspects of the jet propulsion unit accordingto the invention:

[0014] the thrust bearing comprises a bearing housing surrounding andencasing a bearing disc connected to or cooperating with the impellershaft and said bearing housing being arranged axially movable by meansof adjusting devices a distance sufficient for the play between theimpeller blades and the inside of the pump housing to stay within thelimits of a maximally and minimally admissible play of the blades.

[0015] rods are attached at a distance from and parallel with the shaftextending through the bearing housing and that the bearing housing isaxially movable along the rods by means of guides.

[0016] the thrust bearing comprises a bearing housing fixed relative tothe hull of the ship and surrounding and encasing a bearing discconnected to or cooperating with the impeller shaft the bearing discbeing arranged to be axially adjustable by means of adjusting devices adistance sufficient for the play between the impeller blades and theinside of the pump housing to stay within the limits of a maximally andminimally admissible play of the blades.

[0017] the adjusting devices are mounted inside the bearing housing.

[0018] the adjusting devices comprise at least one hydraulic orpneumatic cylinder.

[0019] alternatively, some of or all the adjusting devices may bemechanical adjusting devices.

[0020] the bearing disc is a radially protruding part of the impellershaft, the journal, or an intermediate shaft especially adapted for thethrust bearing and connected to the impeller shaft.

[0021] the bearing housing comprises one or several bearing supports.

[0022] the bearing supports comprise bearing surfaces consisting of e.g.Teflon segments, different composite materials, white metal and/or steeletc.

[0023] the adjusting devices are made of hydraulic or pneumaticcylinders that have a joint of pipe for compressed air and hydraulic oilrespectively through one of the lateral surfaces of the bearing housing.

[0024] the maximally and minimally admissible play of the blades isdeterminated according to real or expected axial and/or radial changesof position of the impeller blades.

ADVANTAGES OF THE INVENTION

[0025] During normal operation, that is, in open sea, with small risk ofstrange objects being sucked in through the pump and during normalweather conditions, the play between the blades of the impeller and theimpeller chamber may be set to a value that is very favourable for theship's propulsion. If the conditions of operation would become worse theplay can be increased temporarily, considerably reducing or fullyeliminating the risk of unwanted wear etc.

DESCRIPTION OF DRAWINGS

[0026] The invention will be explained more in detail with reference tothe attached drawings, wherein:

[0027]FIG. 1. is a schematic longitudinal section through parts of a jetpropulsion unit for propulsion of a ship according to the presentinvention, the jet propulsion unit comprising an impeller moused at theend of an impeller shaft within an impeller chamber.

[0028]FIG. 2 is a schematic longitudinal section through parts of athrust bearing according to a first embodiment, the thrust bearing beingarranged at the impeller shaft according to FIG. 1 and by means of whichan axial movement of the impeller relative the impeller chamber can beaccomplished.

[0029]FIG. 3 is a schematic longitudinal section through parts of athrust bearing according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] With reference to FIG. 1 it is shown schematically and as alongitudinal section parts of a jet propulsion unit 1 for propulsion ofa ship. Being an integrated part of the hull of the ship 2, the jetpropulsion unit 1 comprises an impeller pump 3 with a pump housing 4composed of a front and a rear part and mounted in the stem part 5 ofthe hull of the ship 2 and usually at or alongside the transom stern 6of the hull 2. Furthermore, the impeller pump 3 comprises an impeller 7rotatably journalled at a hub housing 8 centrally and stationary mountedwithin an impeller chamber 9 within the impeller housing 4.

[0031] The impeller housing 4 and its impeller chamber 9 forms a tubesection 10 that is expanded, conical and spherical and attached to aflow tube 11 for sea water. The flow tube 11 extends normally (notshown) in a curve obliquely upwardly from a water-inlet that is arrangedbeneath the load line of the ship and preferably but not necessarily atthe bottom of the ship, further to the inlet opening 12 of the impellerchamber 9 and thereafter astern to a water outlet 13 at the transomstern 6. During operation of the impeller pump 3 a very forceful waterjet S is created projecting through an outlet nozzle 17.

[0032] The hub housing 8 is firmly attached to the pump housing 4 bymeans of several guide rails 14 extending between the inside 15 of thepump housing 4 and the cone-shaped exterior 16 of the hub 8. Said cone16 is pointing astern and forms together with the inside 15 of the pumphousing 4 the outlet opening, i. e. the outlet-nozzle 17, of theimpeller chamber 9.

[0033] Inside the cone-shaped hub 8 there is a bearing seat 18 firmlyattached to the hub 8 via radial rods 19 and arranged to carry a bearingarrangement 20 that may comprise slide bearings or rolling bearings,including combinations of different types of bearings, e.g. spherical,conical or cylindrical thrust bearings and radial bearings. The hub 8can be filled with a lubricant such as oil, thereby being sealed frompenetrating water.

[0034] At the embodiment shown the impeller 7 is attached by a journal21 to an impeller shaft 22, preferably at the end of the journal 21.Alternatively, the impeller 7 may be attached directly to the impellershaft 22. The impeller shaft 22 extends inwardly through the wall of theflow tube 11 at said curve and her into the impeller chamber 9. Theimpeller shaft 22 constitutes either the outer end of the drive shaft ofthe ship or is indirectly connected to the drive shaft. As describedabove, the impeller shaft 22 or the journal 21 are rotatably journalledwithin the hub 8 of the pump housing 4 by means of said bearingarrangement 20.

[0035] The impeller 7 comprises a frustum of a cone 23 facing andattached to the impeller shaft 22 or its journal 21 in such a way thatthe cone part 23 follows the rotation of the impeller shaft 22. Thus,the stationary hub cone 16 and the impeller cone 23 that is rotatablyarranged at the hub cone 16, form together a dome-shaped sphere, aroundwhich the pump housing 4 is shaped to form the likewise sphericalimpeller chamber 9. Several impeller blades 24 are arranged at theexterior of the frustum of a cone 23 for generating the water jet S thatis directed astern. Each impeller blade 24 has such a position and suchan extension, comprising length and angle, relative the impeller cone 23that the distance, below named the play of the blades 25 (or play 25),between the outer periphery of each blade 24 and the inside 15 of thepump housing 4 normally becomes very small relative to the diameter ofthe impeller 7. For example, during normal operation, an impeller 7 withthe diameter of 4.5 meters, may have a play 25 about 0.1% of thediameter of the flow tube 11.

[0036] At the impeller pump 3 shown in FIG. 1 the impeller 7 is mountedon the journal 21 of the impeller shaft 22 and the journal 21 isjournalled in bearings in the hub 8 by means of the bearing arrangement20 schematically shown. In a preferred embodiment, the bearingarrangement 20 comprises one or several slide bearings 26 mounted alongthe journal 21 and/or the impeller shaft 22. Suitably, the slidebearings 26 included consist of continuous radial bearings. The bearingarrangement 20 is carried by said radial rods 19 fixed within the hubcone 16.

[0037] Via the impeller 7, the water jet S directed astern produces aforce of reaction F in the opposite direction that is transferred to theimpeller shaft 22 possibly via the journal 21. This axial force ofreaction F must be transferred to the hull of the ship 2, which is doneby means of thrust bearings 27 in a way more closely described below.Only some limited parts of the shaft 22 are designed to be able to carrythe enormous forces of pressure from the impeller 7 and this is donewith the aid of one or several thrust bearings 27 located at a suitabledistance from the impeller 7 itself.

[0038] Thus, during normal operation all of the axial forces of reactionF of the impeller shaft 22 including all other normally occurring axialforces and/or movements are carried by said thrust bearings 27. The play25 between the impeller blades 24 and the inside 15 of the pump housing4 remains almost constant, at least, all occurring movements stay withinthe limits of the admissible play 25. However, the play 25 might, asdescribed above, be influenced by additional movements or externalforces, that are not to be regarded as normally existing during normaloperation, such as oscillations and vibrations caused by for exampledeformations of the hull of the ship 2 and the impeller shaft 22, toughsea conditions, foreign objects passing through the impeller chamber 9and/or radial changes of position caused by defective mounting of thejet propulsion unit 1 and its propulsion engine. Said oscillations,movements and vibrations might result in such axial and/or radialchanges of position of the impeller blades 24 that they run the risk ofcontacting the inside 15 of the pump housing 4.

[0039] For this reason, either all of the thrust bearings 27 arearranged axially movable, according to a first design of the presentinvention, see FIG. 2, or certain parts of the thrust bearing 27 arearranged axially movable, a distance sufficient making this risknegligible or fully eliminated, according to a second design of theinvention, see FIG. 3.

[0040] The thrust bearing 27 comprises a stabile bearing housing 28surrounding and enclosing a bearing disc 29 that is preferably aradially protruding and circular part of the impeller shaft 22, thejournal 21, or an intermediate shaft 30 especially adapted to the thrustbearing 27. The bearing housing 28 has a first and a second radiallateral surface 31, 32 arranged astern and afore and at the inside ofeach lateral surface 31, 32 one or several bearing supports 33, 34 aremounted. Alternatively, said bearing supports 33, 34 are arranged, alsoor instead, on one or both lateral surfaces 35, 36 of the circularbearing disc 29.

[0041] Also, the bearing housing 28 comprises two sealing flanges 37, 38arranged at each side of the bearing housing 28 and journalled inbearings on the shaft 21, 22, 30 extending through the bearing housing28 and rotating during drive, by means of a separate bearing arrangement39, suitably comprising one or several radial bearings. The bearingsupports (33,34) comprise bearing surfaces (40) consisting of forexample Teflon segments, different composite materials, white metaland/or steel etc.

[0042] In the first embodiment (FIG. 2), the entire thrust bearing 27 isarranged to be axially movable along several rods 42 via several guides41 arranged at the bearing housing 28. The rods 42 are arranged at acertain distance from and parallel with the shaft 21, 22, 30 extendingthrough the bearing housing 28 and they are attached to the hull of theship 2 in a suitable way.

[0043] In front of the bearing housing 28, i. e. afore, there areseveral adjusting devices 43 attached at the hull 2 to achieve the axialmovement astern of the shaft 21, 22, 30, and by that also of theimpeller blades 24, a distance sufficient that the play 25 will be largeenough that the risk that undesired oscillations, movements and/orvibrations will result in such axial and/or radial changes of positionof the impeller blades 24 that they run the risk of contacting theinside 15 of the pump housing 4 will be negligible or fully eliminated.

[0044] Preferably, each adjusting device 43 comprises at least onehydraulic or pneumatic cylinder 44 but some of, or all the adjustingdevices 43 may also be mechanical adjusting devices comprising one orseveral electric engines (not shown).

[0045] Unlike in the first embodiment, the bearing housing 28 in thesecond embodiment (FIG. 3) is fixed to the hull 2 in a suitable way (notshown). Here, the adjusting devices 43 are mounted at the inside of thebearing housing 28, more exactly, between the inside of the aforearranged radial lateral surface 32 of the bearing housing 28 and thebearing disc 29. In the embodiment shown in FIG. 3 the adjusting devices43 are hydraulic or pneumatic cylinders 44 that have a joint of pipe 45for compressed air and hydraulic oil respectively through said lateralsurface 32. However, one, several or all of the adjusting devices 43shown may instead be constituted by the above-mentioned mechanicaladjusting devices. Otherwise, the movement of the bearing disc 29, theshaft 21, 22, 30, the impeller 7, the impeller blades 24 and by that thechange of the play 25 is achieved in the same way as in the above firstembodiment.

[0046] It is understood that when a smaller play 25 is once moredesirable a reduced pressure in the cylinders 44 will result in theforce of reaction from the impeller pump 3 forcing the shaft 21, 22, 30and by that the bearing disc 29 in the thrust bearing 27 afore. However,when mechanical adjusting devices 43 are being used, the change is done,in the same way as the increase of the play 25, but in the oppositedirection. It is understood that in the case the impeller drive is notactivated for achieving the movement afore, additional adjusting devices43 may instead be mounted astern of the bearing housing 28 for achievingthe same function as at the aforedescribed adjusting devices 43, but inthe opposite direction.

Description of Function

[0047] According to the invention, the function and the use of theaxially adjustable or movable thrust bearing 27 for the jet propulsionunit 1 is as follows:

[0048] During normal operation, the force of reaction of the impeller 7is carried by the thrust bearing 27 at the setting of the play 25 thatis suitable for normal operation. The adjusting devices 43 will beactivated either automatically or manually when there is an increasingrisk of damages due to a play 25 that is too small in view of thepresent or expected oscillations, vibrations, movements or conditions,or if such movements etc. are detected. The adjusting devices 43 moveeither the entire bearing housing 28 including the bearing disc 29, orthe bearing disc 29 only, and thereby the shaft 21, 22, 30 astern, whichin its turn increases the play 25 between the impeller blades 24 and theinside 15 of the pump housing 4 due to the spherically shaped and asternwidening impeller chamber 9.

ALTERNATIVE EMBODIMENTS

[0049] Thus, the invention is in no way limited to the specificallydisclosed embodiments, but every other configuration according to theaforedescribed comes within the inventive concept.

[0050] For example, it is understood that instead of a conventional,homogeneous steel shaft the impeller shaft 22 may fully or partlycomprise composite material such as glass fibre, coal fibre, plasticsetc. Furthermore, it is understood that the other parts of the jetpropulsion unit 1, may be made of composite- or light material, such ascoal fibre etc. when it is considered suitable. Bearing surfaces andsurfaces exposed to erosion are suitably provided with preventivecoating, for example by polyurethane. Naturally, combinations of abovementioned materials or of other materials, here not mentioned but withsimilar characteristics, may occur.

[0051] Also, it is understood that when some kind of cylinderarrangement for the movement is used, the design gains a certaindampening function. The above-described bearings comprised by thebearing arrangement 20, 39 may be either water- or oil lubricated.

[0052] Finally, it is understood that also the number, dimensions,material and shape of the elements and details comprised by the jetpropulsion unit 1 must be adapted according to the ship and the otherprevailing demands and conditions. This also applies to the number ofjet unit propulsions 1 mounted at the ship in question.

1. Jet propulsion unit (1) for propulsion of a waterborne craftcomprising at least one impeller pump (3) with a pump housing (4) inbeing an integrated part of the hull which an impeller shaft (22) or ajournal (21) connected to said impeller shaft (22) is rotatablyjournalled in bearings, and an impeller (7), having impeller blades(24), the impeller (7) being fixed to said impeller shaft (22) orjournal (21) so as to follow the rotation of the impeller shaft (22),the impeller blades (24) being arranged at the impeller (7) with a play(25) between each impeller blade (24) and the inside (15) of the pumphousing (4), characterized in that the jet propulsion unit (1) alsocomprises an axially adjustable thrust bearing (27) arranged tocooperate with the impeller shaft (22) for adjusting said play (25), andthat the thrust bearing (27) comprises a bearing housing (28)surrounding and encasing a bearing disc (29) connected to or cooperatingwith the impeller shaft (22).
 2. Jet propulsion unit according to claim1, characterized in that said bearing housing (28) being arranged to beaxially movable by means of adjusting devices (43) a distance sufficientfor the play (25) between the impeller blades (24) and the inside (15)of the pump housing (4) to stay within the limits of a maximally andminimally admissible play of the blades (25).
 3. Jet propulsion unitaccording to claim 2, characterized in that rods (42) are attached at adistance from and parallel with the shaft (21, 22, 30) extending throughthe bearing housing (28) and that the bearing housing (28) is axiallymovable along the rods (42) by means of guides (41).
 4. Jet propulsionunit according to claim 1, characterized in that the thrust bearing (27)comprises a bearing housing (28) fixed relative to the hull of the ship(2) and surrounding and encasing a bearing disc (29) connected to orcooperating with the impeller shaft (22), the bearing disc (29) beingarranged to be axially adjustable by means of adjusting devices (43) adistance sufficient for the play (25) between the impeller blades (24)and the inside (15) of the pump housing (4) to stay within the limits ofa maximally and minimally admissible play of the blades (25).
 5. Jetpropulsion unit according to claim 4, characterized in that theadjusting devices (43) are mounted inside the bearing housing (28). 6.Jet propulsion unit according to any one of claims 2-5, characterized inthat the adjusting devices (43) comprise at least one hydraulic orpneumatic cylinder (44).
 7. Jet propulsion unit according to claim 6,characterized in that some of or all the adjusting devices (43) insteadare made of mechanical adjusting devices (43).
 8. Jet propulsion unitaccording to any one of claims 2-7, characterized in that the bearingdisc (29) is a radially protruding part of the impeller shaft (22), thejournal (21), or at intermediate shaft (30) especially adapted for thethrust bearing (27) and connected to the impeller shaft (22).
 9. Jetpropulsion unit according to any one of claims 2-8, characterized inthat the bearing housing (28) comprises one or several bearing supports(33, 34).
 10. Jet propulsion unit according to claim 9, characterized inthat the bearing supports (33, 34) comprise bearing surfaces (40)consisting of e.g. Teflon segments, different composite materials, whitemetal and/or steel etc.
 11. Jet propulsion unit according to claim 5,characterized in that the adjusting devices (43) are hydraulic orpneumatic cylinders (44) that have a joint of pipe (45) for compressedair and hydraulic oil respectively through one of the lateral surfaces(31, 32) of the bearing housing (28).
 12. Jet propulsion unit accordingto any one of claims 2-11, characterized in that the maximally andminimally admissible play of the blades (25) is determinated accordingto real or expected axial and/or radial changes of position of theimpeller blades (24).